1.2.1 Field of the Invention
The exemplary, illustrative, technology herein relates to systems, and methods for irradiating horticultural products using liquid cooled Light Emitting Diode (LED) lighting systems.
1.2.2 The Related Art
Horticultural products are more frequently grown indoors using artificial lighting. Conventional indoor lighting used to irradiate horticultural products is provided by High Intensity Discharge (HID) lamps which includes metal halide and high pressure sodium (HPS) light bulbs. One problem with the HPS light bulbs is that they operated at high temperatures and therefore emit high levels of thermal radiation that tends to excessively heat the indoor space in which they are being used. Additionally, HPS lamps can generate enough thermal radiation to actually damage the plants and therefore HPS lamps need to be sufficiently spaced apart from the horticultural products, e.g. by at least 2 feet and in some cases up to 4 feet (0.3-0.6 Meters) to avoid damaging the plants.
Typically HPS lamps are housed within a reflective enclosure configured to reflect and redirect useful radiant energy being emitted by the lamp toward the horticultural products. However the thermal energy being emitted by the HPS lamps is absorbed by the reflective enclosure which leads to a need to cool the reflective enclosure using a forced airflow. As a result, most indoor growing spaces illuminated by HPS lamps are climate controlled in order to compensate for the high levels of thermal radiation being generated by operating the HPS lamps. The added cost of operating a climate control system just to remove thermal energy emitted by the illumination system is undesirable.
A further problem with HPS light bulbs is the life expectancy. Typically HPS light bulbs are replaced every six (6) months, and the ballast is replaced once per year. The short life expectancy and frequent replacement of HPS lamps leads to high operating costs and there is a need in the art to reduce irradiation operating costs by providing a longer lasting light source.
Another problem with convention HID discharge lamps is that the spectral power of the emitted radiation is incompatible with the needs of the horticultural products. HID lamps each have a standard spectral power that includes significant radiant energy at wavelengths that provide no useful benefit to horticultural product growth. This is demonstrated in FIG. 8 which provides a graphical comparison (800) between the relative spectral absorption of plant material vs wavelength of the spectral energy and the relative spectral power vs wavelength of a conventional HPS light source.
Photosynthesis relies on pigments (chlorophyll A, chlorophyll B and carotenoids) to absorb light and transfer energy from the absorbed light to the plant. The relative amount of light absorbance by chlorophyll A, chlorophyll B and carotenoids vs wavelength is shown in FIG. 8 in the graphical comparison (800). A first curve, (805) shows the relative absorbance of chlorophyll A vs wavelength. The first curve (805) has a major absorption peak at about 430 nm and another absorption peak at about 700 nm. A second curve (810) shows the relative absorbance of chlorophyll B. The second curve (810) has a main absorption peak at about 460 nm and another absorption peak at about 675 nm. A third curve, (815) shows the relative absorbance of carotenoids vs wavelength. The third curve (815) has a main absorption peak ranging between about 450 and 520 nm and another absorption peak at about 675 nm coincident with an absorption peak of the second curve (810) at about 675 nm.
Thus chlorophyll A, chlorophyll B mainly absorbs violet and blue light at the main absorption peaks and absorb red and deep red light at the secondary absorption peaks. However chlorophyll A and chlorophyll B reflect or transmit green and yellow light having a wavelength spectrum in the range of about 550 to 650 nm. The carotenoids mainly absorb indigo and blue light at the main absorption peak between about 450 and 520 nm and absorb red light at 675 nm. However the carotenoids reflect or transmit yellow and orange light having a wavelength spectrum between about 550 and 650 nm.
To demonstrate the main drawback of conventional HPS light sources used to irradiate horticultural products, the relative spectral power vs. wavelength of a conventional HPS light source is plotted in FIG. 8 on the graphical comparison (800). A fourth curve, (820) shows the relative spectral power vs wavelength of a conventional HPS light source. The fourth curve (820) has a three strong relative spectral power peaks between about 575 and 620 nm with a minor relative spectral power peak between about 460 nm and 480 nm. Thus the majority of the relative spectral power output of a conventional HPS light source is yellow and orange light which is not readily absorbed by any of the three pigments responsible for photosynthesis and is mainly reflected by or transmitted through plant materials. To compensate for this major shortcoming of the conventional indoor lighting systems used to illuminate horticultural products, the HPS lamps are operated at very high power levels to irradiate plant material with enough of the spectral power that is in a useful spectral range for plant growth. In particular, the only spectral power of the HPS lamps that can be absorbed by plant materials is provided by the three minor spectral peaks (830) and the tail of the main spectral peak (835). Otherwise, as is demonstrated by FIG. 8, the majority of the spectral power emitted by the HPS light provides no actual benefit to the plants.
LED lighting systems are known for irradiating plant growth. One such system is disclosed in U.S. Pat. No. 5,012,609 to Ignatuis et al. which describes a plant irradiance system using three different LED lamp types emitting at three different wavelengths. Another such system is disclosed in U.S. Pat. No. 7,933,060 to Dubuc which describes a support structure for uniform light distribution from LED's.